The present invention relates to fiber optic networks, and more particularly to monitoring the performance of fiber optic networks.
Fiber optic networks are becoming increasingly popular for data transmission due to their high speed, high capacity capabilities. As the traffic on fiber optic networks increases, monitoring and management of the networks become increasingly more significant issues. To monitor the network, the spectral characteristics of the composite signal at particular points in the network must be determined and analyzed. This information may then be used to alter the performance of the network if the signal characteristics are less than optimal.
FIG. 1 illustrates one conventional method of determining the spectral characteristics of the composite signal in a fiber optic network utilizing a Fabry-Perot interferometer. The Fabry-Perot interferometer 10 is a mechanical device which scans wavelengths of an optical signal. The Fabry-Perot interferometer 10 comprises two glass plates 11 and 12 exactly parallel and placed at a distance L from each other. The glass plate 11 is a fixed mirror with a partially reflective coating 13 on the side facing glass plate 12. The glass plate 12 is a scanning mirror with a partially reflective coating 14 on the side facing glass plate 11. The two glass plates 11, 12 together form a cavity 15 of length L. An optical fiber 16 inputs collimated polychromatic light into the Fabry-Perot interferometer 10 through the outside face of glass plate 11. Those wavelengths of the light which consist of integral numbers of half wavelengths which can fit in the cavity 15 exit the interferometer 10 from the side opposite optical fiber 16 and are sampled by the photodetector 17. The photodetector 17 can then output the wavelengths for analysis, as illustrated in box 20. All other wavelengths of the light are not transmitted through Fabry-Perot interferometer 10 to receivers 17 due to destructive interference.
However, the Fabry-Perot interferometer 10 can only scan one wavelength at a time. To obtain the entire spectrum of the signal, the Fabry-Perot interferometer must scan by causing the second glass plate 12 to travel back and forth, thereby varying the length L of the cavity 15. The length L is varied so that each wavelength of the spectrum can be sampled by the photodetector 17. Precision mechanical positioners 18 are used to move the second glass plate 12. This scanning can require up to several seconds to accomplish due to the fact that the Fabry-Perot interferometer 10 is a mechanical device. The response time of the conventional system is thus slow. Also, the conventional system is difficult to align since the glass plates 11, 12 must be exactly parallel in order to obtain the correct spectrum. Fabry-Perot interferometers are well known in the art and will not be further discussed here.
Accordingly, there exists a need for method and system for a performance monitor in a fiber optic network which is faster than conventional performance monitors. The performance monitor should be just as accurate as conventional performance monitors and allow the spectrum to be obtained in fractions of a second, allowing for real-time performance monitoring. The present invention addresses such a need.
The present invention provides a method and system for monitoring a composite optical signal in an optical network. The method includes separating the composite optical signal into a plurality of subsets where each subset includes a plurality of data points, and detecting the plurality of data points. The method and system in accordance with the present invention utilizes an optical performance monitor which is able to obtain the entire spectrum in a matter of milliseconds and is limited by optical switching speed or computing power or speed. The system can be readily improved, if necessary, to provide faster measurement speed, resolution, or accuracy. The preferred embodiment of the optical performance monitor utilizes a plurality of channel separator or dense wavelength division multiplexer modules to separate sets of data points of the optical signal and transfer these data points to a device for analysis. The method and system of the present invention is faster than conventional performance monitors. Because the optical performance monitor of the present invention allows the spectrum to be obtained in fractions of a second, real-time performance monitoring is provided. Furthermore, because a plurality of data points are time multiplexed onto each and every optical detector via optical switch settings, the method and system of the present invention is cost effective. The optical performance monitor may be combined with another device in the optical network to control the performance of the network.